Re: [PATCH v3] xen: Allow a default compiled-in command line using Kconfig

[Julien Grall <julien.grall@arm.com>]

Hi Jan,

On 03/07/2017 02:52 PM, Jan Beulich wrote:
>>>> On 07.03.17 at 15:41, <julien.grall@arm.com> wrote:
>> Hi Jan,
>>
>> On 03/07/2017 02:18 PM, Jan Beulich wrote:
>>>>>> On 07.03.17 at 14:48, <julien.grall@arm.com> wrote:
>>>> On 03/07/2017 12:52 PM, Jan Beulich wrote:
>>>>>>>> On 07.03.17 at 12:21, <blackskygg@gmail.com> wrote:
>>>>>> 2017-03-07 17:36 GMT+08:00 Jan Beulich <JBeulich@suse.com>:
>>>>>>>>>> On 07.03.17 at 09:34, <blackskygg@gmail.com> wrote:
>>>>>>>> +static inline char* __init extract_dom0_options(char *cmdline)
>>>>>>>> +{
>>>>>>>> +    char *kextra;
>>>>>>>> +
>>>>>>>> +    if ( (kextra = strstr(cmdline, " -- ")) != NULL )
>>>>>>>> +    {
>>>>>>>> +        *kextra = '\0';
>>>>>>>> +        kextra += 3;
>>>>>>>> +        while ( kextra[1] == ' ' ) kextra++;
>>>>>>>
>>>>>>> The body of the while() wants to go on its own line.
>>>>>>>
>>>>>>> And then - why is this Dom0 option handling done only on x86?
>>>>>>>
>>>>>>
>>>>>> As you might have noticed, there isn't any code dealing with the dom0
>> options
>>>>>> in arch/arm/setup.c, and the arm version of construct_dom0() doesn't take
>> any
>>>>>> command line options as its parameter,
>>>>>> so I have the reason to believe that this feature is not available
>>>>>> under the arm architecture.
>>>>>
>>>>> Looks like an omission to me - Julien, Stefano?
>>>>
>>>> DOM0 and Xen command line are passed separately through either Device
>>>> Tree or for UEFI xen configuration file (see -cfg=...).
>>>>
>>>> So I am not sure to understand what would be the benefits to handle DOM0
>>>> parameters after -- on Xen command line.
>>>
>>> So you have no case of a boot loader which allows you to type in
>>> extra options on just a single line? On x86 the feature had originally
>>> been added because old grub didn't have a separate line for Dom0
>>> options in its graphical menu. Nowadays the functionality is handy
>>> namely when starting xen.efi from the EFI shell (where again you
>>> obviously only have a single command line), but quite likely this may
>>> also be of use with grub's chain loading model (which I simply don't
>>> use very often, so I'm not finally sure on that one).
>>
>> My knowledge is quite limited on boot process for x86. How do you pass
>> the kernel/initrd/xsm blob on UEFI? Can you do it from the command line
>> or are you using the -cfg=... and specify it in a file?
>
> Only the latter.
>
>> On ARM we have two way to boot Xen:
>> 	- Using UEFI bootloader with either Device-Tree or ACPI
>> 	- Using non-UEFI bootloader with Device-Tree only
>>
>> In the case of UEFI bootloader, we are using the xen configuration file
>> to describe the modules (e.g kernel, initramfs, XSM) and the both xen
>> and DOM0 command line.
>>
>> For non-UEFI bootloader, we have designed the boot protocol based on the
>> device-tree and will allows you to specify both xen and DOM0 and all the
>> modules (see [1]). The bootloader needs to be able to modify the
>> device-tree (such via a shell like on U-boot) or the user needs to
>> modify the device-tree before hand.
>
> All fine, but this doesn't tell me what interactive change options a
> user has _after_ having set up the config file (or alike), while the
> system is booting.

Here some concrete examples. The major bootloaders on ARM today are:
	* UEFI
	* U-boot
	* GRUB

I will leave UEFI aside as people will usually chainload to GRUB and 
then boot whatever they want.

In both GRUB and U-boot a user will be able to modify the command line 
from the bootloader shell.

Cheers,

-- 
Julien Grall

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